Reducing hf-water phase disposal in alkylation

ABSTRACT

A method and apparatus for processing a hydrogen fluoridecontaining, analyzed catalytic fluid, separating therefrom a hydrogen fluoride-water phase and recycling or disposing of said phase in response to the concentration of water in the analyzed fluid relative to a desired value of said concentration.

waited States Patent 1191 Cannady et al.

[541 REDUCING HF-WATER PHASE 3,273,576 9/1966 Fluegel et al ..137/2DISPOSAL IN ALKYLATION 3,031,105 4 1962 Walker ..137 119 [75] Inventors:William P. Cannady; Joe Van Pool,

both of Bartlesvine, Ok1a Primary Exammer-Delbert E. Gantz A b P l CAssistant ExaminerG. J. Crasanakis 811; and 911% [22] Filed: Mar. 26,1971 [57] ABSTRACT [21] Appl. No.: 128,383 A method and apparatus forprocessing a hydrogen fluoride-containing, analyzed catalytic fluid,separat- 52 US. c1 ..260/683.48, 208/DIG. 1 ing theefmm hydmgenflmide'water Phase and [51] Int. Cl ..C07c 3/54 recycling sp sing ofSaid phase in response to the [58] Field of Search ..260/683.48-, 137/2,concentration of water in the analyzed fluid relative to 137/1 19 adesired value of said concentration.

[56] References Cited 4 Claims 2 Drawing Figures UNITED STATES PATENTS3,410,759 11/1968 Fontenot et al. ..260/683.48

ANALYZER SEPARATING 22 VESSEL LLC a 36 RECYCLE TO SYSTEM 8 2 as I TO 1DISPOSAL PATENTED APR 1 01973 ATTORA/[Fy REDUCING IIF-WATER PHASEDISPOSAL IN ALKYLATION In a hydrogen fluoride catalyzed alkylationsystem for the reaction of olefins with isoparaffins, the acid catalystcomprises a liquid mixture of hydrogen fluoride, acid-soluble oil, andwater. These systems are well known by those skilled in the art ofhydrogen fluoride alkylation.

In the operation of a hydrogen fluoride alkylation system, the acidcatalyst can be separated and recovered from hydrocarbons beingprocessed by passing the mixture into an acid settling tank. For thepurpose of refortification of the catalyst, a portion of the acid phaseis passed to a rerun distillation column where a portion of thereconcentrated hydrogen fluoride is taken off as overhead product andreturned to the acid system, and a mixture comprising acid-soluble oil,water, and a decreased amount of hydrogen fluoride is discharged fromthe lower portion of said column. This mixture is generally dischargedfrom the alkylation system and disposed of.

Disposal of this mixed acid-oil stream has presented problems owing tothe toxicity of the hydrogen fluoride contained in said stream. In orderto reduce the labor, equipment, and other expenditures required toproperly dispose of this toxic fluid and better protect the environmentfrom accidental toxic damage from this fluid, a unique handling methodand apparatus has been discovered.

The method and apparatus of this invention comprises passing the fluidmixture to a liquid separating vessel, separating the acid-soluble oilphase from the hydrogen fluoride-water phase of said mixture andrecycling to the catalytic system said hydrogen fluoride-water phase inresponse to a fluid analysis indicating a concentration of water lessthan a preselected value.

Other aspects, objects, and advantages of the present invention willbecome apparent from a study of the disclosure, the appended claims, andthe drawings.

The drawings are diagrammatic views of the apparatus of this inventionand a portion of the associated apparatus of a hydrogen fluoridealkylation system.

FIG. 1 shows an embodiment of the apparatus and the controls thereof,and

FIG. 2 shows a portion of the apparatus with controls of anotherembodiment.

Referring to FIG. 1, an acid settling vessel 1 of the acid system of ahydrogen fluoride alkylation system has a conduit 2 attached to a lowerportion thereof for the passage of a fluid mixture comprisingacid-soluble oil, hydrogen fluoride and water from the'acid settler l toa rerun column 3. This mixture comprises, for example, about 90 percentby weight hydrogen fluoride, 2 percent water, and 8 percent acid-solubleoil.

In the rerun column 3, a portion of the hydrogen fluoride is separatedby distillation from the mixture, recovered, and recycled to the acidsystem to refortify same as is known in the art.

A separating vessel 6 is connected to the lower portion of the reruncolumn by a conduit 4 for the passage of a mixture of acid-soluble oil,hydrogen fluoride, and water from the rerun column to the separatingvessel 6. This mixture has a reduced concentration of hydrogen fluoridetherein, for example about 35 percent or less. The separating vessel 6has a chamber 5, upper and lower portions 7,8 and a middle portion 10with said conduit 4 connected to the separating vessel in communicationwith the chamber at preferably the middle portion thereof.

In separating vessel 6, the acid-soluble oil phase is 7 liquid levelcontroller 13 associated with the lower portion of column 3 to maintaina desired liquid level therein.

A second conduit 16 is connected to the lower portion 8 of theseparating vessel 6 for discharging the hydrogen fluoride-water phasetherefrom.

An analyzer 18, preferably a water concentration analyzer, is locatedand samples upstream of the rerun column 3 and/or from the acid phase ofsettler 1 for analyzing the fluid upstream of said rerun column anddelivering a signal through line 20 that is representative of the waterconcentration in said fluid.

A controller 22 is connected to the analyzer through line 20 forreceiving the signal from the analyzer, comparing said signal to apreselected set point, and delivering a controlling signal through line24 responsive to that comparison.

A third conduit 26 connects conduit 16 with the settler 1 for recyclingthe hydrogen fluoride-water phase thereto and a fourth conduit 28connected to conduit 16 is provided for passing said hydrogenfluoride-water phase to disposal.

A flow controlling means, here shown as first and second valves 30, 32,is connected to the second conduit 16 and respective third and fourthconduits 26,28 for selectively directing fluid flowing through thesecond conduit into either the third or fourth conduit 26,28. The flowcontrolling means can also be a threeway valve as known in the art.

The first and second valves 30,32 are operationally connected to line 24for receiving a signal from the controller. The first and second valves30,32 are constructed so that upon receipt of the control signal throughline 24 as produced by controller 22 responsive to the comparisontherein of an analysis lower in value than the set point of thecontroller 22, the first valve 30 is opened and the second valve 32 isclosed and upon receipt of the signal as produced by controller 22responsive to the comparison therein of an analysis higher in value thanthe set point of the controller 22, the first valve 30 is closed and thesecond valve 32 is opened. This technique may be described as opposed orsplit range valve operation, such as employing two control valves, oneof which is normally open, the other being normally closed, eachcalibrated to begin to operate at about mid scale of the output ofcontroller 22.

During normal operation, the first valve 30 is generally open, thesecond valve is generally closed, and a liquid level controller 34,monitoring and controlling the interface between the acid-soluble oilphase and the hydrogen fluoride-water phase, positions valve 36associated with separating vessel 6 thereby controlling the removal ofhydrogen fluoride-water phase from the separating vessel through thethird conduit 26 back to the acid system. Where an excessive waterconcentration is detected in the system by the analyzer 18 resultingfrom a water leak into the system, for example, the hydrogenfluoride-water stream is discharged from the system in order to preventcorrosion and degradation of the reaction in said system. The set pointof the controller 22 is of a value preferably representative of theoptimum water concentration of the fluid stream flowing through conduit2 into the rerun column, for example a value representative of about 2weight percent water.

It should be understood, however, that the concentrations of the othercomponents in the stream can be analyzed and the detected totalconcentration subtracted from the whole (100 percent) to obtain theconcentration of water in said stream, but for simplicity it ispreferred that the analyzer be a water analyzer such as disclosed inU.S. Pat. No. 3,424,975.

Referring to FIG. 2, a pump 38, preferably a centrifugal pump, isassociated with the second conduit 16, the first valve 30 is a normallyopen valve operatively connected to the controller 22, and the secondvalve 32 is a back-pressure-controlled, normally closed valve. Thesecond valve 32 of this embodiment has associated therewith aconventional pressure measuring means 40 connected to the second conduit16 downstream of the pump 38 and is connected to a conventionalcontrolling means 42 of the second valve 32 for opening valve 32 inresponse to a pressure within said second conduit 16 greater than thepressure set point of said controlling means 42, so that when pump 38discharges the hydrogen fluoride-water stream 16 from vessel 8 inaccordance'with liquid level controller 34 and valve 36, and valve 30 isclosed by virtue of higher-than-desired water concentration in the acidcatalyst, then controller 42 via valve 32 takes action to discharge thisstream to disposal means not shown.

Here the analyzer is in communication with the lower portion of the acidsettling tank. An example pressure set point of the controlling means 42of this embodiment may be 100 psi.

In the method of this invention, the above-described fluid mixturepasses from the lower portion of an acid settling vessel 1, for example,into a rerun column where a portion of the hydrogen fluoride isseparated and removed therefrom. The water, acid-soluble oil, andremaining hydrogen fluoride is thereafter discharged into the chamber ofthe separating vessel 6.

1n the separating vessel 6, the acid-soluble oil phase is separated fromthe hydrogen fluoride-water phase and said oil is recovered therefrom.The separated hydrogen fluoride-water phase is discharged from theseparating vessel 6 through the second conduit 16 by opening of thecontrolling valve 36 in response to upward movement of the interface .12between the oil phase and the hydrogen fluoride-water phase. Thiscontrolling valve 36 and associated equipment maintains the interface 12at a preselected height within the separating vessel 6 for optimumseparation of the fluid phases therein.

The feedstream to the rerun column or the fluid in the lower portion ofthe acid settling vessel is analyzed by the analyzer and a signalrepresentative of that analysis is delivered through line 20 to acontroller 22. In

controller 22 the received signal is compared to a preselected set pointand a controlling signal responsive to that comparison is delivered tothe valve means.

In the embodiment shown in FIG. 1, the first valve 30 is maintained inan open position and the second valve is maintained in a closed positionduring receipt of a signal from the controller 22 representative of awater content analysis less than the set point of the controller 22.This causes the hydrogen fluoride-water phase to be recycled to thesystem thereby avoiding disposal problems and toxic dangers. Where theanalyzer 18 detects a water content greater in value then the set pointof the controller 22, said controller functions to close the first valve30 and open the second valve, thereby directing the hydrogenfluoride-water phase to disposal. As described above, this fluid isgenerally directed to disposal only where the upstream equipment hasmalfunctioned. It should be understood that the valves can also bemanually operated to reduce the amount of fluid in said system wheredesired.

In the embodiment shown in FIG. 2, a pump 38 operates to deliver fluidfrom the separating column into the second conduit 16. An interfaceliquid level controller is associated with the column and an associatedcontrolling valve 36 is positioned downstream of the pump 38 formaintaining the interface 12 at a preselected elevation within theseparating column. The pressure downstream of the pump is measured bythe pressure measuring means 40 and a signal representative of thatpressure is delivered to the controlling means 42 of the second valve32. The first valve 30 receives a signal from the controller 22 andassociated analyzer 18 as set forth above.

During receipt of a signal representative of an analyzed water contentless than the set point of the controller 22, the first valve 30 remainsnormally open and the second valve 32 remains normally closed therebyrecycling fluid from the separating column to the acid system. Uponreceipt of a signal from the controller 22 representative of an analyzedwater content greater than the set point of the controller, the firstvalve 30 is caused to close. Since pump 38 is continuously operating,the pressure measured by the pressure measuring means 40 increases to avalue greater than the set point of the controlling means 42 at whichtime the second valve 32 is caused to open and the fluid is dischargedto disposal. Owing to the pressure sensitive control of the second valve32, the fluid discharging from the separating column is also diverted todisposal where the third conduit 26 or other associated downstreamequipment becomes plugged and the pressure as measured by the pressuremeasuring means 40 increases to or above the preselected value.

The apparatus and method of this invention therefore provides for theseparation of the acid-soluble oil phase from the hydrogenfluoride-water phase thereby conditioning said hydrogen fluoride-waterphase for recycle to the system under preselected conditions therebyprotecting the system against undue contamination but also to reduce theproblems associated with the costly disposing of a toxic and potentiallyvaluable hydrogen fluoride-containing stream.

Other modifications and alterations of this invention will becomeapparent to those skilled in the art from the foregoing discussion andaccompanying drawing and it should be understood that this invention isnot to be unduly limited thereto.

What is claimed is:

l. A method for reducing the amount of hydrogen fluoride and waterdisposal from a hydrogen fluoride alkylation system having a reruncolumn with a feedstream flowing thereinto, comprising:

passing a first stream comprising acid-soluble oil,

hydrogen fluoride, and water from the rerun column into a separatingvessel;

separating the acid-soluble oil from the hydrogen fluoride-water phasewithin the separating vessel; discharging the hydrogen fluoride-waterphase from the separating vessel;

analyzing the feedstream of the rerun column to determine the watercontent thereof;

passing a signal representative of the analysis to a controller;

comparing the signal to a preselected set point in the controller andestablishing a control signal representative of the differencetherebetween;

recycling the hydrogen fluoride-water phase discharging from theseparating column back to the hydrogen fluoride alkylation system inresponse to the control signal indicating a water content less than thepreselected set point; and

discharging the hydrogen fluoride-water phase from the hydrogen fluoridealkylation system in response to the control signal indicating a watercontent greater than the preselected set point.

2. A method, as set forth in claim 1, including maintaining an interfacebetween the acid-soluble oil and the hydrogen fluoride-water phase at apreselected height within the separating vessel.

3. A method, as set forth in claim 1, wherein the feedstream of thererun column is analyzed at an acid settling vessel positioned upstreamof the rerun column and in communication therewith.

4. A method, as set forth in claim 1, wherein the set point isrepresentative of a water content of about 2 percent by weight.

2. A method, as set forth in claim 1, including maintaining an interfacebetween the acid-soluble oil and the hydrogen fluoride-water phase at apreselected height within the separating vessel.
 3. A method, as setforth in claim 1, wherein the feedstream of the rerun column is analyzedat an acid settling vessel positioned upstream of the rerun column andin communication therewith.
 4. A method, as set forth in claim 1,wherein the set point is representative of a water content of about 2percent by weight.